General observation of the contour of the head is important, since molding occurs in almost all vaginal deliveries. In a vertex delivery the head usually is flattened at the forehead, with the apex rising and forming a point at the end of the parietal bones and the posterior skull or occiput dropping abruptly. The usual more oval contour of the head is apparent by 1 to 2 days after birth. The change in shape occurs because the bones of the cranium are not fused, allowing for overlapping of the edges of these bones to accommodate to the size of the birth canal during delivery, such molding does not occur in infants born by cesarean section.
Basic Anatomy of the head bones
Six bones-the frontal, occipital, two parietals, and two temporals-comprise the cranium. Between the junctions of these bones are bands of connective tissue called sutures. At the junction of the sutures are wider spaces of unossified membranes tissues called fontanels. The two most prominent fontanels in infants are the anterior fontanel formed by the junction of the sagittal, coronal, and frontal sutures, and the posterior fontanel, formed by the junction of the sagittal and lambdoidal sutures. One can easily remember the location of the sutures because the coronal suture “crowns” the head and the sagittal suture “separates” the head.
Two other fontanels- the sphenoidal and mastoid are normally present but are not usually palpable. An additional fontanel located between the anterior and posterior fontanels along the sagittal suture is found in some normal neonates but is also found in some infants with Down’s syndrome. The presence of this sagittal or parietal fontanel is always recorded.
Clinical assessment
The doctor palpates the skull for all patent sutures and fontanels, noting size, shape, molding or abnormal closure. The sutures are felt as cracks between the skull bones, and the fontanels are felt as wider “soft spots” at the junction of the sutures. These are palpated by using the tip of the index finger and running it along the ends of the bones.
The size of anterior fontanel is assessed between middle points of the opposite sides of the fontanel (between the frontal and parietal bones). The anterior fontanel is diamond-shaped, measuring 2.5cm (1 inch) by 3cm (about 1.5inches). The posterior fontanel is triangular- shaped, measuring between 0.% and 1cm (less than1/2 inch) at its widest part. It is easily located by following the sagittal suture towards the occiput.
The fontanels should feel flat, firm and well-demarcated against the bony edges of the skull. Frequently pulsations are visible at the anterior fontanel. Coughing, crying, or lying down may temporarily cause the fontanels to bulge and become more taut. However, a widened, tense, bulging fontanel is a sign of increased intracranial pressure. A markedly sunken, depressed fontanel is an indication of dehydration. Such findings are recorded and reported to the physician.
The doctor also palpates the skull for any unusual masses or prominences, particularly those resulting from birth trauma, such as caput succedaneum or cephal-hematoma, because of the pliability of the skull, exerting pressure at the margin of the parietal and occipital similar to the indentation of a ping-pong ball. This phenomenon is known as physiologic craniotabes and, although usually a normal finding, can be indicative of hydrocephalus, syphilis and ricket.
The degree of the head control in the neonate is also assessed. Although the head lag is normal in the newborn, the degree of the ability to control the head in certain positions should be recognized. If the supine infant is pulled from the arms into a semi-Fowler’s position, a marked head lag and hyperextension are noted. However, as one continues to bring the infant forward into a sitting position, the infant attempts to control the head in an upright position. As the head falls forward onto the chest, many infants try to get to the erect position. If the infant is held in ventral suspension, that is, held prone above and parallel to the examining surface, the infant holds his head in a straight line with the spinal column, when lying on the abdomen, the newborn has the ability to lift the head slightly, turning it from side to side.
A marked head lag is seen in Down’s syndrome, hypoxic infants, and newborns with brain damage which are diagnosed by specific head peculiarities.